• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

A WE-91B project

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Hi guys, a friend ask me to make a valve amp for him, I want to use WE-91B, since his speaker is TAD2402(sensitivity:93dB). He want to use 300B, so I think WE-91B is a good choice
1.jpg

this is the circuit I draw in Altium Designer, because I want to make it into PCB
2.JPG
some of the components has been set to 91B accroding the original schematic

It is impossible for to collect the original WE components to make this amp, so I deceided to use morden components to make it.
 
first of all, deceided the power trans T3(359A)
3.JPG

the WE documents of 359A
4.jpg

prim: 110V+120V
sec:492.5+492.5/130mA
10V/1.2A(for 310A*2)
5V/2A(for 274B)
5V/2.4A(for 300B)

since I will not use 91B in excitaion speaker system, it is not necessary to keep 492.5+492.5

my design is
prim:220V
sec:400V+400V/130mA
10V/1.2A(for 310A*2)
5V/2A(for 274B)
5V/2.4A(for 300B)
 
I believe it is actually NFB due to the way it is feed back to the screen instead of the grid, and taken from the plate of the output tube.

Note 7 seems to confirm this in stating that shorting the 70K feedback resistor results in 10dB less gain. Shorting the 70K feedback resistor allows more feedback.
 
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